This invention relates to a hitch adapter for connecting a tractor drawbar to the tongue of a trailing implement wherein the vertical pivot axis between the tractor and the implement is located equidistantly between the front and rear universal joints of a power takeoff hookup assembly that connects the tractor power takeoff to the implement driveshaft.
A hitch adapter of the above general type is disclosed in U.S. Pat. No. 3,557,892, which is also assigned to the assignee herein.
As described in said patent, the location of the vertical pivot point equidistantly between the front and rear universal joints is highly desirable to provide equal angles of articulation at the front and rear universal joints when there is articulation about a vertical axis between the implement and the tractor, to thereby provide constant speed in the drive train eliminating speed variations and vibrations in the drive system.
One of the problems with such hitch adapters resides in the fact that the sizes of the tractor drawbars vary widely according to the size of the tractor and the manufacturer of the tractor. Accordingly, since the hitch adapter must be laterally rigid with the tractor drawbar, it has been found necessary to provide some type of adjustment in the hitch adapter so that it can be mounted on different size drawbars. In said U.S. Pat. No. 3,557,892, said adjustment is accomplished by providing vertical bolts that are adjustable along angled slots to vary the spacing between the bolts, the bolts engaging the opposite sides of the drawbar to vary the effective width of the cavity in the adapter housing that receives the drawbar. However, since the entire towing force between the tractor and the implement is transmitted through the hitch adapter, relatively large forces are involved, and it has been found that the forces are sufficiently large to frequently shift the bolts and thereby loosen the adapter on the drawbar. Of course, the tighter the bolts are tightened, the greater the resistance to such shifting, but is has been found that it is difficult to obtain sufficient torque on the bolts and nuts to prevent the lateral sliding of the bolts with conventional tools readily available to the farmer when adjusting the adapter for a particular tractor drawbar.